The invention concerns plastic sheeting based on polymers of propylene and ethylene, which may also contain processing aids, fillers, pigments or other additives, and their use in the form of self-adhesive decorative sheets for coating any objects or molded articles.
Surface sheets for laminating of any objects appear in European Patent Application 0 343 491. These sheets are intended to be applied to the surfaces of objects, such as doors, shelves, or cabinets, of plastic, wood, wood derivatives, metals, or similar materials or substrates in colored, uncolored, or patterned form to provide protection against various undesirable effects such as corrosion, discoloration by light or mechanical action. Under some circumstances they are intended to be shaped to match the surface of the object in question. For instance, such a patterned sheet laminated onto a surface can give the impression of a valuable wood, even on an object that is not suitable for that because of its nature, structure, surface or color. The surface sheeting seen from European Patent Aplication 0 343 491 has a base sheet of a polymer of the methacrylate group. The polymer can be modified by addition of polyacrylates. A polymethyl methacrylate (PMMA) plasticized by polybutyl methacrylate (PBMA) is said to be particularly suitable. The known surface sheeting is said to have improved resistance to light and weathering. It has been found, in testing this sheeting, that it needs improvement. For instance, a plasticized PMMA exhibits relatively high white break or white crackling. Even if this material is modified for high impact, it still has only low impact resistance. It also has unsatisfactorily low wettability or surface tension values. High surface tension values are important for the printability of the basic sheet and for its sticking ability (adhesion between an adhesive layer and the basic sheet). For example, a basic sheet of PMMA has a surface tension of only 36 to 38 dyn/cm (measured according to DIN 53 364).
A sheet of the type indicated initially appears in German Laid-Open Patent 41 21 599. It has a base sheet that contains an ethylene-propylene copolymer, containing processing aids and/or additives and if desired, at least one dye-pigment mixture and/or filler. An adhesive layer is applied to the under surface or underside of the base sheet, along with, if necessary, a cover sheet or release sheet. If desired, the base sheet can have embossing and/or a color-printed layer. The ethylene-propylene polymer used in the 50 to 150 .mu.m thick base sheet has a melt flow index (230.degree. C., 2 kg) of more than 3 g/10 minutes and a tensile strength greater than 30 N/mm.sup.2. This sheet is used as a self-adhesive decorative sheet to coat glass, panels, paper, cardboard and other objects or molded articles of metal, wood, or wood derivatives. The known sheet is said to have a Shore hardness D of 55 to 70. Because of the specific starting materials, this known sheeting does not have satisfactory stiffness. The stiffness is important when such a sheet is used to laminate wood and other parts. High stiffness reduces the sensitivity of the laminated sheet to writing and scratches.